Beyond coping with rapid population growth and its related social-economical challenges, urban areas become increasingly vulnerable to climate change patterns. In order to mitigate the consequences, Natural-based solutions (NBS) tackle the root cause of the problem - the abandonment of natural spaces in favor of built-up areas. By restoring or stimulating nature throughout cities, this modern concept benefits from the provided ecosystem services, such as heat mitigation, runoff reduction, air quality improvement or even community well-being. However, awareness of these advantages has not spread yet among stakeholders, due to the lack of data on effectiveness and costs of such solutions worldwide.
This thesis is thus in line with the promotion of NBS through the quantification and communication of their benefits to urban planning bodies. It proposes a natural-oriented concept for the drainage system of the future neighborhood of Gaswerkareal - Bern. Additionally, the project’s impact on urban heat islands (UHI) and retention capacity is assessed using the InVEST platform. Through simplified bio-physical modeling, this software maps and values the desired outcomes, therefore contributing to enhance exchanges between experts and decision makers. In parallel, the models performances are discussed to highlight their potential and limitation for small urban sites applications.
With the main objective of reducing the high runoff risk of the perimeter to 10% of the incoming rainfall, one third of the impervious cover is replaced by gardens, green spaces (yards and rooftops), infiltration basins and pervious pavements. To further control the released runoff peaks and volumes, three retention volumes are subtly dimensioned and positioned to align with the site’s physical-chemical properties and to optimize the trade-off between storage performance and land use interests. The designed scenario shows three times greater retention capacity than the actual situation, according to the 43-years long rainfall data built simulation. Two-thirds of this increase can be attributed to changes in land cover, as confirmed by the InVEST flood mitigation module’s results. However, while the SCS-CN method is a widely used and reliable runoff estimator for small catchments, it yields mixed results when applied to closely homogeneous surfaces, particularly in urban environments, as evidenced by the simulated retention of the actual site.
Despite the promotion of green spaces, forests and green roofs, the Urban cooling module relates limited cooling potential for daily conditions, typically below 1 C◦, emphasizing the need for larger scale intervention to achieve more significant outcomes. At night, temperature changes are more noticeable, though predominantly higher due to the density of buildings. However, the model faces great uncertainties induced by the maximum cooling and the air blending distances parameters. A better characterization of macro-urban air and heat flu
